The invention relates to an electron gun for generating an electron beam, comprising a cathode unit composed of a cathode shaft which is surrounded by a heat reflection screen, which cathode shaft is secured to a holder containing electron-emitting material having an emissive surface.
The invention also relates to a method of manufacturing an electron gun comprising a cathode unit, in which a cathode shaft is suspended in a heat reflection screen and a holder containing electron-emitting material is secured to the head end of the cathode shaft, and to a display tube having such an electron gun.
An electron gun of the type mentioned in the opening paragraph is used in black-and-white and colour display tubes for television and data display, in camera tubes and other tubes in which an electron beam is to be generated. The life of such tubes is largely determined by the life of the electron gun, which is governed by, inter alia, the life of the cathode unit of the electron gun and the suspension of the cathode unit in the heat reflection screen. Moreover, it should be possible to mass-produce accurately an electron gun, in particular the cathode unit, having a short warm-up time. The present developments in the field of electron guns are aimed at meeting these requirements. However, it has been found in practice that the electron guns known so far still have several disadvantages.
An electron gun of the type mentioned in the opening paragraph is known from U.S. Pat. No. 4,403,169 (PHN 9733). In the Patent Specification a description is given of an electron gun in which the cathode shaft is suspended in the heat reflection screen so as to be self-supporting by means of relatively long metal wires one end of which is secured to the end of the cathode shaft near the emissive surface and the other end is secured to a cathode support member which is located outside the reflection screen. In practice it has been found, however, that the operation and the life of the electron gun are sensitive to vibrations.